U.S. Pat. No. 6,073,524 (“the '524 Patent”) and U.S. Pat. No. 6,135,680 (“the '680 Patent”) provide good background and context for the present development, the contents of which are fully incorporated herein by reference. The present development pertains to the lateral stabilization of a boring tool as metal cutting element (or elements) carried by the tool enter, traverse, and emerge from a generally circularly cylindrical passage. The passage is defined in a metal work piece and usually is open at its opposite ends. When undergoing the machining process of boring, the diameter of the passage is increased to a specified diameter; the machined passage is then called a “bore.” Another effect of the boring process is to cause the surface of the bore to be a machined surface; the surface of the initial passage may not be a machined surface, as the initial work piece can be a casting for an automotive engine block and the boring process is used to form piston cylinders in the block.
The '524 Patent describes a boring tool 8 in which there are three metal cutting elements 10 carried at the “head” or “lead” end 12 of a rotatable tool body 14 (also known as a “bar”) at locations spaced substantially equally about the circumference of the tool body. The cutting elements 10 are disclosed to be circular things called “inserts” or “teeth” which are so carried in the tool that they rotate in a self-propelled manner about their central axes in response to forces applied to them as they operate on a work piece to remove metal from the work piece in the course of creating a desired bore. The bore is formed as the tool is rotated about its own axis and is advanced into a work piece passage which is to be machined into a bore. The '680 Patent describes such a boring tool in which the self-propelled rotary inserts are mounted in the tool body to have axial and radial stagger as shown best in FIG. 3 of that patent.
An examination of the cited patents reveals that the boring tool can have substantial length 18 between its lead end 12 and its opposite trailing end 16 where it is configured to be held in a power-driven chuck of a boring machine. The forces applied to the boring tool as its first “lead” cutting element first engages the work piece can cause the lead end of the tool to be deflected laterally, causing a dynamic effect called “chatter.” When chatter occurs, the lead cutting element does not form a truly circularly cylindrical surface in the work piece and the surface formed in the work piece may not have a desired dimension or a finish characteristic. The chatter situation described above is “entrance chatter” which occurs as the boring tool enters into machining engagement with a work piece.
Chatter can continue to occur as the second (“intermediate” or “mid”) cutting element advances into contact with the work piece, with similar results. Chatter effects can increase as the third (“finish”) cutting element advances into contact with the work piece.
A similar chatter situation called “exit chatter” can occur as a boring tool advances to move the lead cutting element, and then the intermediate cutting element beyond the far or exit end of the bore. Further, chatter can occur when all cutting elements are operating on the work piece. Once chatter begins to occur, it can continue throughout the boring process.
It is rare that a machined surface created under chatter conditions meets acceptable finish and dimensional requirements. Furthermore, dynamic chatter effects impose shock-like high-frequency cyclic loads upon the boring tool, notably on the cutting elements and the structures which mount them to the tool body, as well as (to a more attenuated extent) upon the boring machine itself. Such chatter effect loads reduce the useful lives of the things on which they are imposed, and so, they are to be avoided, minimized, and reduced in duration and magnitude to the greatest extent possible.